Method and device for pressure amplification in cylinders, in particular hydraulic rams

ABSTRACT

A method and corresponding cylinder for pressure amplification in cylinders are disclosed. A second pressurizing piston with a small piston rod is arranged within the cylinder, in other words, within the cylinder housing, by means of which the piston surface cavity in the vicinity of the piston or the pressure medium present there can be further compressed. It is thus possible to increase the stroke displacement where required or to increase the pressure within the cylinder. Further advantages can also be achieved with the above.

The invention relates to a method for increasing pressure in cylindersused for oil hydraulic, water hydraulic, emulsion hydraulic as well asplasma and other fluid hydraulic systems, in which two part ormulti-part cylinders are moved apart or together in a controlled fashionby means of valves, and the introduced pressure transducer, which haspassed a high pressure pump, whereby in the piston surface cavitybeneath the respective piston a specified pressure, even afterseparation from one another, is generated and maintained throughcompression of the piston surface cavity. The invention moreover relatesto a cylinder for performing the method according to claim 1, comprisinga foundation with cylinder housing, the body being connected to a highpressure pump via a supply line, as well as a piston/piston roddisplaceable therein and the piston surface cavity formed beneath thepiston between the cylinder cover and piston, piston rod and cylinderhousing, as well as a compressor that can be inserted in the pistonsurface cavity, and the piston surface cavity formed beneath the piston.

When actuating cylinders and similar devices, the movement is created byfeeding a pressure-transmitting agent, involving oil, water, water in anoil emulsion, plasma or other fluids or also air. By hydraulics is meantthe theory and technical application of flows in compressible fluids.This means that in hydraulic systems, the fluid, above all oil or alsowater in an oil emulsion, initially must be appropriately acted upon ina high pressure pump, i.e. it is prestressed, and is then supplied tothe cylinder via hoses or similar lines. The extension and theretraction of the cylinders is controlled by means of valves, alwaysoccurring at one and the same pressure level, namely the pressure levelthat is dependent upon the output of the high pressure pump. Especiallyin underground mining, where water in an oil emulsion is used for safetyreasons, at present 400 bar max. is used, simply because currently nopumps are available which are able to generate a higher pressure level.Due to various circumstances, however, it is not always guaranteed thatthe afore-mentioned pressure is available in the piston surface cavity,so so-called adjustment circuits are known in underground mining andtunnel construction which allow the volume in the piston surface cavityto be adjusted through re-connection to the high pressure pump such thatthe above-mentioned pressure level is approximately available. It is notpossible, however, to generate a higher pressure level within the pistonsurface cavity and hence within the cylinder because, as said before,said pumps are not in a position to do so. Yet for various reasons thisis frequently desirable, with the pumps in the case of theaforementioned current highest pressure level of 400 bar representing alimit, while in the case of a lower pressure level, the costs of anadditional high pressure pump and corresponding hoses would essentiallyonce again compensate for the advantage.

The invention is therefore based on the object of creating a method anda device which enable the operation of cylinders at a randomly increasedinternal pressure (operating pressure) in relation to the pump pressure.

The object is achieved from a method point of view in that the cylinderis first fed a pressure-transmitting medium (oil, water, emulsion,plasma, compressed air) at a specified pressure level, based on whichthe cylinder can be displaced, and that thereupon the pressure in thepiston surface cavity beneath the piston is increased randomly by usingthe pressure-transmitting medium having the same pressure level tofurther compress the pressure-transmitting medium in the piston surfacecavity.

This method hence makes it possible to increase the pressure levelwithin the piston surface cavity in a specific manner, regardless of thestarting point of the pressure level of the pressure transducer, so asto achieve advantages. When for example proceeding from a pressure levelthat is clearly below 400 bar, the method according to the inventionallows the pressure level in the cylinder to be increased in a specificmanner without requiring other lines, a cylinder with differentdimensions or another pump. Rather the pressure within the cylinder isincreased such that the desired maximum pressure level is reached. Thisway for example in underground mining and tunnel construction, thenecessary input pressure in the stamp, i.e. the appropriately designedcylinder, can be achieved without requiring the use of an expensive highpressure pump, which also accordingly requires special lines and valves.Rather, a less expensive and simpler high pressure pump reaching acorrespondingly lower pressure level can be used in order to stillattain the desired pressure level inside the cylinder or stamp by usingthe method. Of course it is also possible for the first time to exceedthe 400 bar pressure level because with appropriate pressure applicationon the compressor/tensioning piston this pressure transducer allows aclearly increased pressure level to be generated within the cylinder soas to be able to accomplish the desired objectives. It is possible, forexample, to use the invention to achieve a higher pressure in a specificmanner or travel a longer path. The cylinders need not be modified. Ifhowever as explained above a lower pressure level is assumed, also inthe area of the stamp, but especially in the hoses, thinner walls andsimpler designs may be used so as to reduce the investment costs. It isnow also possible to use the plug-in connections especially popular inunderground mining and tunnel construction even when operating at higherend pressures. On the other hand, using hoses with a larger diameter,operation may occur at a lower pressure level in order to achieve thespecific amount of pressure transducer fed this way or set it at a veryhigh level.

According to an appropriate embodiment of the invention, it is providedthat the pressure-transmitting medium is fed to the cylinder by a 200bar pump and that the pressure in the piston surface cavity is increasedto 300-400 bar or more. This is accomplished with a pressure increasesystem, which is mentioned up front here and shall be explained furtherbelow and allows the pressure level inside the cylinder to be increasedcorrespondingly easily and reliably and as a function of the dimensions.

According to a further development, it is correspondingly provided thatthe volume of the piston surface cavity is reduced by feeding thepressure-transmitting medium and hence increased compression of thepressure-transmitting medium is generated. The pressure-transmittingmedium is accordingly compressed further without the need forintroducing pressure-transmitting medium, hence an oil or compressedair, at a higher level. That means that no separate or other pump isrequired, and accordingly a different system pressure. This has theaforementioned advantages, but additionally also the benefit that it canbe implemented easily and without difficulty.

The invention will lead to an increase in the pressure level inside thecylinder, which is accomplished according to the invention in that apiston with smaller dimensions is inserted at the same pressure throughthe pressure-transmitting medium into the piston surface cavity,compressing the pressure-transmitting medium located there. Thisincreases the pressure level tremendously and in a manner as is requiredfor the respective application.

Depending on the area of application, the invention provides accordingto its method that the pressure-transmitting medium having the samepressure level is connected as a function of other switch processes orseparately so as to keep the possibly required switch complexity as lowas possible.

Again, depending on the case and area of application, the inventionmakes it possible that the pressure-transmitting medium having the samepressure level is connected in series or parallel, which is enabledamong other things in that no second system pressure exists and is notrequired for increasing the pressure or the pressure level in a specificmanner beneath the piston.

A cylinder is provided for implementing the method, which has a cylinderhousing and the piston displaceable therein with a piston rod, whereinthe piston surface cavity is formed beneath the piston, in which thehydraulic fluid or pressure-transmitting medium is fed so as to achievethe displacement of the cylinder. A variable pressure level inside thepiston surface cavity is achieved in that the piston surface cavity,specifically the pressure-transmitting medium located therein, isdesigned such that it can be influenced using the same high-pressurepump directly via an input valve and additionally indirectly via acompressor. It has already been mentioned above that the compressor is apressure increase system, which hence ensures that the higher pressurein the piston surface cavity is in fact achievable, even if thepressure-transmitting medium required or used for this has acorrespondingly lower pressure level. A specific change in the pressurelevel inside the piston surface cavity is made possible for the firsttime with the invention described, above all of course to increase it,in particular to above the value enabled by the present high-pressurepumps.

An appropriate embodiment of the invention is that in which the pistonsurface cavity is designed as boreholes incorporated in the cylindercover, piston and piston rod, wherein the borehole in the piston rod isexpanded so as to accommodate a bushing in which the tensioning pistonwith a small piston rod (which corresponds to the borehole) is arrangeddisplaceably, and can be connected on the head side to the samehigh-pressure pump by means of a connecting valve. Already theenumeration of the individual parts of the pressure increase makes itclear that here a solution is provided, which leads to a goal that waspreviously not even considered in an astonishingly simple manner.Without changing the pressure level of the employed high-pressure pumpit is possible to increase the pressure level within the piston surfacecavity, i.e. within the cylinder, such that additional functions can befulfilled, without requiring changes to the device.

The piston surface cavity is for one connected directly to the highpressure pump and secondly indirectly, whereby it is provided that thepiston surface cavity can be connected directly to the high pressurepump via the input valve arranged on the head side of the piston. Withrespect to underground use in a figurative sense, the input valve istherefore located in the base region of the stamp or the cylinder sothat the piston with the piston rod can be safely moved out when theconnection to the high pressure pump has been established because thenthe piston is experiencing pressure across an accordingly large surface.

The tensioning piston, which is arranged displaceably inside thecylinder, is supplied from above with hydraulic fluid, i.e. the pressuretransducer—again viewed visually and based on the example of anunderground stamp. According to the invention, it is provided that thebushing accommodating the tensioning piston is closed by a rod head,which simultaneously closes the large piston rod, to which connectingboreholes that connect the connecting valve and tensioning piston on thehead side are allocated. This rod head is inserted partially into thebushing or the correspondingly large piston rod and fixed there, whereinit is held in this position already due to the fact that it is clampedin place from above and/or pressure is applied from above. Theconnecting valve hence rises with the rod head, however remains easilyaccessible at all times, because it projects laterally beyond the rodhead or the piston rod. This way, it is ensured that also the additionalpressure in the cylinder can be created, using one and the same pressuretransducer, in terms of the pressure level. The pressure transducer isconducted to the tensioning piston on the head side via the connectingvalve and the connecting boreholes so that said piston can be displacedaccordingly, as forced by the specified surfaces. The tensioning pistonhas appropriate dimensions; it is significantly larger than the pistonrod.

The rod head, which closes the bushing at the top and hence also thehollow large piston rod, incidentally ensures that the pressureconditions inside the cylinder can be built up appropriately.

In order to ensure appropriate compression in the piston surface cavity,it is provided that the tensioning piston comprises a plate-shapedrecess on the head side. This plate-shaped recess ensures that thepressure fluid or the pressure-transmitting fluid can spread evenlyacross the largest possible surface of the piston. It also prevents thetensioning piston from practically sticking to the rod head. Overall,this arrangement ensures a fast, reliable response of the correspondingpressure increase system.

It had already been pointed out further above that the tensioning pistonhas a significantly larger diameter than the associated small pistonrod. In particular, the piston rod has a diameter of 68 mm, and thetensioning piston has a diameter of 110 mm. The piston surface cavity bycontrast has a diameter of 70 mm, which will be addressed hereinafter.

In accordance with the dimensions mentioned above, a selectively annulargap remains, wherein the invention provides that the small piston rod isdesigned such that an annular gap remains between it and the boreholewall of the piston, which is connected to the bottom of the bushingbottom through which the small piston rod can travel. This way, wheninserting the small piston rod in the borehole, pressure fluid isdisplaced through the annular gap, ensuring that appropriate pressure isapplied to the bushing bottom so that this rod is displaced in thelongitudinal direction of the cylinder, carrying the rod head with it.

An appropriate further refinement provides that the bushing bottom has astepped design, wherein the lower small step comprises effective sealingrings in relation to the outer wall of the small piston rod and theinner wall of the large piston rod. While initially this offers only asmall surface for the additionally compressed pressure transducer, thissurface increases as the bushing is lifted out of the second seat sothat the second step then becomes effective.

On the basis of the dimensions indicated above, but also on the basis ofthe basic effect, it is apparent that the tensioning piston has a largerdiameter than the small piston rod, thus forming in the bushing an airring cavity that contains air. When inserting the tensioning piston andthe small piston rod, the air contained therein must be displaceable,which is accomplished in that the bushing in the area of the bushingbottom comprises a cross borehole, connecting the air ring cavitybetween the bushing inside wall and the outside wall of the small pistonrod with a longitudinal borehole to the outside atmosphere. Whenretracting the tensioning piston and the small piston rod, the air isthus pushed into the longitudinal borehole without difficulty via thecross-hole, and from there it can be discharged to the outsideatmosphere. With the reversed process, air will enter the air ringcavity via the outside atmosphere and the longitudinal borehole as wellas the cross-hole, so that the tensioning piston and the small pistonrod can be pushed safely back into the initial position.

Pressure transducer or hydraulic fluid is applied to the large pistonfrom beneath for the purpose of retracting the cylinder. This isaccomplished especially expediently in that between the inside wall ofthe cylinder housing and the outside wall of the large piston rod anannular cavity is formed, which is closed towards the bottom by thepiston with the sealing rings and towards the top by a clamp collar withintegrated sealing rings, which can be connected to the same highpressure pump via a leveling valve. Thus, if the connection to the highpressure pump is established via the leveling valve, the pressuretransducer directly enters the annular cavity, during which process thesealing rings ensure that the annular cavity is sealed to the outside.In this way, the pressure transducer affects exclusively the bottom ofthe large piston, so that said piston is moved back into the startingposition.

In order to be able to position the clamp collar securely, it isprovided that the clamp collar has available an outside thread, which isdesigned such that it corresponds to the inside thread associated withthe cylinder housing end. The clamp collar can then be screwed in andassumes a secure position, even if the cylinder is being moved out orretracted.

Despite the relatively high pressure building up on the inside of thecylinder, it is sufficient if the sealing rings allocated to the clampcollar are arranged in a sealing fashion in relation to the large pistonrod and the annular cavity. It is useful if the clamp collar comprisestwo sealing rings as well as a third one that is directed downward, i.e.in the direction of the annular cavity.

The invention is especially distinguished in that a method and a deviceare created which basically simplify the operation of cylinders.Operation may occur either with pumps of low output, whereby then therequired pressure increase is performed in the cylinder, or one canoperate with the same units, especially the high pressure pumpsgenerating the highest pressure and can then generate a considerablyhigher pressure beyond this inside the cylinder, which either offers anincreased travel or increased pressure within the cylinder. Overall, themethod and device offer specialists the opportunity to simplify existinghydraulic systems or compressed air systems, managing with lessexpensive hoses having thinner walls, and possibly also withcorresponding cylinders, or also to create such a high pressure levelthat this way the above-described advantages can be achieved, usingexisting hoses.

Further details and advantages of the object of the invention resultfrom the following description of the corresponding drawing, whichillustrates a preferred embodiment including the necessary details andindividual parts, wherein:

FIG. 1 is a longitudinal section through a cylinder with a pressureincrease system,

FIG. 2 is a shield-type support comprising several cylinders, to be usedin underground mining, and

FIG. 3 is an excavator, which likewise comprises several cylinders.

FIG. 1 shows a cylinder 1 in the longitudinal section, whereby itbecomes clear that the foundation 2 of this cylinder 1 comprises acylinder housing 3 with a cylinder cover 4 and a piston 5 with a pistonrod 6. The piston 5 with the piston rod 6 is arranged displaceablyinside the cylinder housing 3, with the supply line 7 feeding hydraulicfluid or pressure transducer into a piston surface cavity 8 via an inputvalve 9. This pressure transducer penetrating into the piston surfacecavity 8 ensures that the piston 5 with the piston rod 6 and the rodhead 19 at the end travels out of the cylinder housing 3. The inside,here referred to as a compressor 10, does not impair this movementand/or supports it.

The piston surface cavity 8 in the illustrated example is formed by theborehole 11 in the cylinder cover 4, the borehole 12 in the piston 5 andthe borehole 13 in the piston rod 6. The piston surface cavity 8 hencehas the shape of a cylinder.

The large piston rod 6 is hollow, as already mentioned, with theborehole 13 extending all the way to the upper end. A bushing 15 isarranged in this borehole 13, which holds a tensioning piston 16 withthe small piston rod 17. The tensioning piston 16 is arrangeddisplaceably in the longitudinal direction, wherein it can be connectedto the supply line 7′ and the high pressure pump, which is not shownhere, via a connecting valve 18 attached to the rod head 19 and theconnecting boreholes 20, 21. The pressure transducer is hence conductedfrom the supply line 7 into the connecting valve 18 and from there viathe two connecting boreholes 20, 21 to the tensioning piston 16, whichin this area comprises a plate-shaped recess 22. In this way, it isensured that the inflowing hydraulic fluid, i.e. the pressuretransducer, can apply pressure on the entire surface of the tensioningpiston 16. Seals 23, 24 are disposed on the edge of the tensioningpiston 15, which ensure the necessary sealing effect and guarantee thatthe pressure transducer can apply pressure on the tensioning piston 16all the way to the bushing 15. The correspondingly large diameter of thetensioning piston 16 then ensures that in the case of an appropriateload applied by the typical pressure transducer, i.e. the typicalpressure level of the pressure transducer, the tensioning piston 16 andthe small piston rod 17 can be pushed forward in the direction of thepiston surface cavity 8. In doing so, the small piston rod 17 displacesthe pressure transducer present in the piston surface cavity 8 and/orcompresses it. Only when an additionally increased pressure exists inthe piston surface cavity 8 will the hydraulic fluid orpressure-transmitting fluid also apply pressure on the bottom 29 of thebushing borehole 30 via the annular gap 26 between the borehole wall 27of the piston 5 and the outside wall 28 of the small piston rod 17. Thiseffect or influence increases further if the bushing 15 due to thepressure conditions has moved along with the rod head 19 because thebushing bottom 30 comprises two steps 31, 32. Sealing rings 34, 35 arearranged in the bushing bottom 30 such that for one they seal theconfiguration against the inside wall 33 of the large piston rod 6, andsecondly against the outside wall 28 of the small piston rod 17.

It is recognizable in FIG. 1 that due to the different dimensions of thetensioning piston 16 and the small piston rod 17, an annular air space37 remains between the latter and the bushing inside wall 38, this spacebeing connected via a cross-hole 40 to a longitudinal borehole 39, whichleads in the direction of the atmosphere because it exits the bushing 15at its end. This offers the possibility that air can escape from the airring cavity 37 through the cross-hole 40 and the longitudinal borehole39 when retracting the tensioning piston 16. Conversely, it canpenetrate again into the air ring cavity 37 the opposite way, i.e.through the longitudinal borehole 39 and the cross-hole 40 when slidingthe tensioning piston 16 with the small piston rod 17 back.

An annular space 45 is provided between the inside wall 43 of thecylinder housing 3 and the outside wall 44 of the large piston rod 6 forthe purpose of retracting the piston 5 with the large piston rod 6. Thisannular space 45 extends to beneath the piston 5. The annular space 45is connected via a cross-hole 42 to the retracting valve 52 so thatpressure transducer may be fed into this annular space 45 via the supplyline 7″, if needed. This ensures that the piston 5 with the large pistonrod 6 is pushed back into the starting position illustrated in FIG. 1due to the pressure relief in the area of the input valve 9. In order toensure the effect of the pressure, transducer seal rings 46, 47 areprovided in the piston 5, which on one hand are supposed to provide aseal against the annular space 45 and on the other hand against theinput valve 9.

The annular space 45 is connected to the cylinder housing end 55 via aclamp collar 48, which is equipped with several sealing rings 49, 50, 51so as to provide a seal in relation to all sides. It comprises anoutside thread 54, which is designed to correspond to the inside thread56 of the cylinder housing end 55, enabling it to be screwed in.

FIG. 2 shows a shield-type support 60, comprising several cylindersdescribed below. Especially in underground mining and tunnelconstruction, a safety standard is achieved using a water-in-oilhydraulic system which is excellent in terms of the employed fluid aswell as the achievable input pressure. The goods are transported away bymeans of the conveying equipment 61, wherein this conveying equipment 61extends in the direction of the background and vice versa and isconnected to the base plate 63 of the shield-type support via a pushcylinder 62. The conveying equipment 61 is constantly influenced bymeans of the shifting jack 62 that is rests closely against the coalface, which is not shown here. Extending from the base plate 63, theshield 64 is connected to several lemniscate arms 65 so as to be able toassume an optimal position to the footwall at all times. The stamp orstamps 66, in this case a multi-part stamp, are supplied with hydraulicfluid of about 360-400 bar via a supply line running through thelongwall. These stamps 66, as is explained more below, are connecteddirectly and indirectly to the high pressure pump via the connectingvalve 67. However, only one supply line is required for this, which inparticular can have a simplified design when the cylinder, i.e. thestamp 66 and also the remaining cylinders are designed as illustrated inFIG. 1. The shield 64 is followed by the hanging wall cap 68, which issupported by the stamp 66. The front part of this hanging wall cap 68 isformed by the sliding part 69, which can likewise be inserted anddisplaced using a cylinder, which is not illustrated here, in order tobring the tip 72 of the hanging wall cap 68 as close as possible to thecoal face. Such a longwall construction extends between the hanging wall70 and footwall 71 and ensures that the space remains open as long as isrequired for extraction.

FIG. 3 shows in a simplified form a hydraulic excavator 73 with itstraveling part 74 and the swivel arm 75. Cylinders are allocated to theswivel arm 75, however, as well as to the bucket 77 and other componentswhich allow the individual functions to be performed or facilitated.Using the adjusting cylinder 76, the lower part of the swivel arm 75 isswiveled up or brought into a different position, while the bucket 77 iscontrolled in its movements via the bucket cylinder 78. Both with suchhydraulic excavators 73 and with longwall construction 60 the use of thepresent invention is particularly interesting because a plurality ofcylinders is employed, which also have other functions. Therefore it isnot absolutely necessary to equip all cylinders with an interiorcompressor.

All aforementioned features which can be inferred solely from thedrawings are considered essentially for the invention alone and incombination.

1. Method for increasing pressure in cylinders used for oil hydraulic,water hydraulic, emulsion hydraulic systems as well as plasma and otherfluid hydraulic systems, in which two part or multi-part cylinders aremoved apart or together in a controlled fashion by means of valves andthe introduced pressure-transmitting agent, having passed a highpressure pump, with a specified pressure being generated and maintained,by means of compressing the piston surface cavity, in the piston surfacecavity beneath the respective piston, even after pushing the pistonsapart, wherein the cylinder, specifically its piston surface cavity, isinitially fed a pressure transducer (oil, water, emulsion, plasma,compressed air) and the cylinder is hence moved apart, and wherein thepressure in the piston surface cavity beneath the piston is randomlyincreased by using the pressure transducers of a specified pressurelevel for compression of the pressure transducer in the piston surfacecavity in that a different piston is inserted in the piston surfacecavity with the help of the pressure transducer having a specifiedpressure level.
 2. Cylinder for implementing the method according toclaim 1, comprising a foundation (2), which is connected to a highpressure pump via a supply line (7), with a cylinder housing (3) and apiston/piston rod (5, 6) displaceable therein, and the piston surfacecavity (8) formed beneath the piston (5) between the cylinder cover (4)and piston (5), piston rod (6) as well as the cylinder housing (3) aswell as a compressor (10), which can be inserted in the piston surfacecavity (8), wherein the compressor (10) is designed as a tensioningpiston (16) with a small piston rod (17), is arranged displaceablywithin the piston surface cavity (8) serving as the compressor and canbe connected on the head side of the tensioning piston (16) with apressure-pressure pump.
 3. Cylinder according to claim 2, characterizedin that the piston surface cavity (8) is designed as a borehole (11, 12,13) incorporated in the cylinder cover (4), piston (5) and piston rod(6), with the borehole (13) in the piston rod (6) being expanded suchthat it accommodates a bushing (15), in which the tensioning piston (16)with a smaller piston rod (17) corresponding in its diameter to theborehole (11, 12, 13) is arranged displaceably.
 4. Cylinder according toclaim 2, characterized in that the piston surface cavity (8) can beconnected directly to the high pressure pump via the input valve (9)arranged on the head side of the piston (5).
 5. Cylinder according toclaim 3, characterized in that the bushing (15) accommodating thetensioning piston (16) is closed by a rod head (19), which at the sametime also closes the large piston rod (6) which are allocated connectingboreholes (20, 21) linking the connecting valve (18) and tensioningpiston (16) on the head side.
 6. Cylinder according to claim 2,characterized in that the tensioning piston (16) comprises aplate-shaped recess (22) on the head side.
 7. Cylinder according toclaim 2, characterized in that the tensioning piston (16) has a clearlylarger diameter compared to the allocated small piston rod (17). 8.Cylinder according to claim 1, characterized in that the small pistonrod (17) is designed such that an annular gap (26) is formed between itand the borehole wall (27) of the piston (5), said gap being connectedto the bottom (29) of the bushing bottom (30) through which the smallpiston rod (17) can travel.
 9. Cylinder according to claim 8,characterized in that the bushing bottom (30) has a stepped design, withthe lower smaller step (31) comprising effective sealing rings (34, 35)towards the outside wall (28) of the small piston rod (17) and theinside wall (33) of the large piston rod (6).
 10. Cylinder according toclaim 1, characterized in that the bushing (15) in the area of thebushing bottom (30) comprises a cross-hole (40) connecting the air ringcavity (37) between the bushing inside wall (38) and outside wall (28)of the small piston rod (17) with a longitudinal borehole (39) to theoutside atmosphere.
 11. Cylinder according to claim 1, characterized inthat between the inside wall (43) of the cylinder housing (3) and theoutside wall (44) of the large piston rod (6) an annular cavity (45) isformed, which is closed towards the bottom by the piston (5) withsealing rings (46, 47) and to the top with a clamp collar (48) withintegrated sealing rings (49, 50, 51), which can be connected to thesame high pressure pump via a leveling valve (52).
 12. Cylinderaccording to claim 11, characterized in that the clamp collar (48)comprises an outside thread, which is designed to correspond to aninside thread (56) allocated to the cylinder housing end (55). 13.Cylinder according to claim 11, characterized in that the sealing rings(49, 50, 51) associated with the clamp collar (48) are designed in asealing fashion towards the large piston rod (6) and towards the annularcavity (45).